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SubjectRe: [PATCH 1/5] Add pagetable allocation notifiers
Chris Wright wrote:

>* Zachary Amsden (zach@vmware.com) wrote:
>
>
>>--- linux-2.6.13.orig/arch/i386/mm/init.c 2005-08-24 09:31:05.000000000 -0700
>>+++ linux-2.6.13/arch/i386/mm/init.c 2005-08-24 09:31:31.000000000 -0700
>>@@ -79,6 +79,7 @@ static pte_t * __init one_page_table_ini
>> {
>> if (pmd_none(*pmd)) {
>> pte_t *page_table = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
>>+ SetPagePTE(virt_to_page(page_table));
>>
>>
>
>Xen has this on one_md_table_init() as well for pmd.
>
>

I'll add that in another patch. It's easy to miss some of the init time
call sites (we don't actually depend on them for correctness).


>> spin_lock_irqsave(&pgd_lock, flags);
>> pgd_list_del(pgd);
>> spin_unlock_irqrestore(&pgd_lock, flags);
>>@@ -244,13 +246,16 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
>> pmd_t *pmd = kmem_cache_alloc(pmd_cache, GFP_KERNEL);
>> if (!pmd)
>> goto out_oom;
>>+ SetPagePDE(virt_to_page(pmd));
>> set_pgd(&pgd[i], __pgd(1 + __pa(pmd)));
>> }
>> return pgd;
>>
>> out_oom:
>>- for (i--; i >= 0; i--)
>>+ for (i--; i >= 0; i--) {
>>+ ClearPagePDE(pfn_to_page(pgd_val(pgd[i]) >> PAGE_SHIFT));
>>
>>
>
>Is that the right pfn? That -1 throws me off.
>
>
>
>> kmem_cache_free(pmd_cache, (void *)__va(pgd_val(pgd[i])-1));
>>+ }
>> kmem_cache_free(pgd_cache, pgd);
>> return NULL;
>> }
>>@@ -261,8 +266,10 @@ void pgd_free(pgd_t *pgd)
>>
>> /* in the PAE case user pgd entries are overwritten before usage */
>> if (PTRS_PER_PMD > 1)
>>- for (i = 0; i < USER_PTRS_PER_PGD; ++i)
>>- kmem_cache_free(pmd_cache, (void *)__va(pgd_val(pgd[i])-1));
>>+ for (i = 0; i < USER_PTRS_PER_PGD; ++i) {
>>+ ClearPagePDE(pfn_to_page(pgd_val(pgd[i]) >> PAGE_SHIFT));
>>+ kmem_cache_free(pmd_cache, (void *)__va(pgd_val(pgd[i]) & PAGE_MASK));
>>
>>
>
>Why the switch of kmem_cache_free call?
>
>

Because pgd_val(pgd[i])-1 is confusing. Using (pgd_val(pgd[i]) -
_PAGE_PRESENT) would be better, but the +/- 1s all over the place here
could use some general cleanup as well. I smell a cleanup fit coming
on. Using (pgd_val(pgd[i]) & PAGE_MASK) is a less error prone way to
get the physical frame bits, since it is not wrong if you turn on PCD or
PWD.

Zach
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